The present invention relates to a process for the preparation of polymethylsilsequioxane. More particularly, the present invention relates to a process for the preparation of polymethylsilsesquioxane powder having an improved flow property.
It is well known in the art that a polymethylsilsesquioxane is obtained by hydrolytic condensation of a trifunctional silane such as methyltrichlorosilane. For example, Belgian Pat. No. 572,412 discloses that methyltrichlorosilane is hydrolyzed by spraying it or adding it dropwise to a large quantity of water to obtain a solid polymethylsilsesquioxane. However, this process has disadvantages in that the rise of temperature owing to the exothermic hydrolysis reaction is great, that a large quantity of hydrogen chloride is generated as a by-product causing corrosion of the apparatus and that the polymethylsilsesquioxane obtained according to the process contains trace amounts of hydrogen chloride as by-product and unhydrolyzed methyltrichlorosilane, so that the chlorine content of the polymethylsilsesquioxane is relatively high. Additionally, the production efficiency of this process is not good because a large quantity of water is needed.
To overcome the disadvantages described above, Japanese Patent Laid-Open No. 72300/1979 proposed that methyltrialkoxysilane and/or its partial hydrolyzate having a chlorine content of from 0.1 to 5.0% by weight is hydrolyzed and condensed in an aqueous solution of an alkaline earth metal hydroxide or an alkali metal carbonate. However, a polymethylsilsesquioxane obtained according to this process contains a relatively large amount of alkaline earth metals or alkali metals. Therefore, when it is used as a filler for a variety of synthetic resins, the resulting compositions tend to be hygroscopic. Furthermore, in this process, the chlorine content of the starting material, i.e. methyltrialkoxysilane, must be controlled to be from 0.1 to 5.0% by weight.